8.25.16 Lecture

Question 1

Biological membranes are primarily composed of ___ and ___; what is the ratio of these two components?

Answer 1

Lipids; proteins; on average, 50:50, although proteins can range from 25%-75%

Question 2

Why are biological membranes important?

Answer 2

Membranes function as efficient barriers for diffusion, preventing the mixing of distinct environments, allowing for compartmentalization, and ultimately making life possible.

Question 3

What is the most abundant membrane lipid?

Answer 3

Phospholipid

Question 4

Describe the general structure of phospholipid.

Answer 4

1 polar head (exposed charge), 2 long fatty acid tails attached to a 3 carbon backbone (often carbon or sphingosine)

Question 5

What dictates membrane fluidity?

Answer 5

Length and saturation of fatty acids

Question 6

What is cholesterol?

Answer 6

A lipid molecule present in large amounts in plasma membranes; has a polar head group, rigid steroid ring structure, and nonpolar hydrocarbon tail

Question 7

Increasing membrane rigidity has what effect on the permeability of the bilayer to water soluble molecules?

Answer 7

Decreases permeability

Question 8

Hydrophobic molecules self-aggregate in water. Why?

Answer 8

Self-aggregation is energetically favorable because it is less costly than organizing water molecules around the hydrophobic surfaces of individual lipids.

Question 9

What dictates the shape of the micelle?

Answer 9

The shape of the lipid

Question 10

What explains the ability of a membrane to spontaneously reseal when torn?

Answer 10

Self-aggregation

Question 11

Self-aggregation also provides tremendous ___ to membranes, helping to prevent rupture under stress.

Answer 11

Plasticity

Question 12

What type of movement is common in lipids in membranes?

Answer 12

Lateral diffusion

Question 13

Fluidity of a membranes depends on what two factors?

Answer 13

Lipid composition and temperature

Question 14

What is membrane fluidity?

Answer 14

The relative mobility of lipids within a membrane

Question 15

What is transition temperature?

Answer 15

The temperature at which homogenous lipid bilayer transitions from a liquid state to a more solid gel state (“freezing”)

Question 16

More fluid membranes have a ___ transition temperature.

Answer 16

Lower

Question 17

How is transition temperature lowered and fluidity increased?

Answer 17

Increase double bonds (introduces kinks), decrease length of hydrocarbon tails.

Question 18

What is the difference between saturated and unsaturated chains?

Answer 18

Unsaturated chains have cis double bonds; saturated chains do not.

Question 19

What are lipid rafts?

Answer 19

A type of microdomain; Cholesterol and sphingolipid rich regions of transient self-associations caused by van der Waals forces and associated with cell signaling.

Question 20

Where are glycolipids always found?

Answer 20

On the monolayer facing away from the cytosol

Question 21

Where are negatively charged phospholipids found?

Answer 21

On the cytosolic side

Question 22

What are needed to move phospholipids between monolayer?

Answer 22

Translocases and flipases

Question 23

What are glycolipids?

Answer 23

Glycosylated phopholipids

Question 24

Glycolipids exhibit extreme ___.

Answer 24

Asymmetry

Question 25

Where are glycolipids generated?

Answer 25

The lumen of the Golgi

Question 26

How is apoptosis triggered?

Answer 26

Phosphotidylserine translocates to the exterior membrane in apoptotic cells by scramblase and lack of activity of PS-translocases

Question 27

Lipid bilayer constituents drive ___ through what two general methods?

Answer 27

Signal transduction; acting as a scaffold or as a second messenger

Question 28

Bilayers have both hydrophobic and hydrophilic regions. Transmembranes proteins have similar properties. Where do the various amino acids localize?

Answer 28

Hydrophobic amino acids interact with the core of the bilayer and are buried in the membrane. Hydrophilic amino acids are located on the inner and outer membranes, though polar amino acids can be found in the membranes.

Question 29

What are the general types of proteins?

Answer 29

1. Transmembrane proteins (typically alpha helices)
2. Transmembrane proteins that span multiple times
3. Transmembrane proteins (beta barrels)
4. Amphipathic proteins
5. Proteins modified with a moiety
6. GPI-linked proteins

Question 30

What provides a hydrophobic anchor that keeps proteins associated with bilayers without inserting into the bilayer itself? What are the three kinds of anchors?

Answer 30

Fatty acid modifications of proteins; myrisotyl, palmitoyl, farnesyl

Question 31

What can help determine the presence of a transmembrane protein?

Answer 31

Hydropathy plots

Question 32

___% of proteins are likely membrane proteins.

Answer 32

30

Question 33

What form large pores in the lipid bilayer?

Answer 33

Beta barrels

Question 34

Many membrane proteins diffuse ___ along the bilayer plane. Others are anchored via ___ proteins.

Answer 34

Laterally; cytoskeleton

Question 35

Cell-to-cell communication occurs via a combination of…

Answer 35

…membrane biophysics and cytoskeletal organization, which create dynamic membrane behavior critical for many cellular activities.